Cancer of unknown primary is when the origin of the cancer is unknown. Learn more with this 3D animation. 

What is cancer of unknown primary?

Cancer occurs when cells become abnormal and grow uncontrollably. These cells build-up to form a mass (or lump). 
Cancer of unknown primary in the head and neck region occurs when the origin of the cancer is unknown, but is found to have spread to the lymph nodes in the neck. It accounts for 3–5% of all head and neck cancers.

Most cancers that spread to the lymph nodes of the neck come from flat-shaped cells that line areas such as the inside of the mouth, nose and throat. These cancers are called squamous cell cancers (SCC). Only a minority of cancer cases come from the salivary glands and other structures; another source are skin cancers, where squamous cells are also found.

What causes cancer of the unknown primary?

Doctors often can't explain why a person gets cancer. However, the main causes of head and neck cancers and cancer of unknown primary are:

  • alcohol and smoking (cigarettes, cigars or pipes) or using ‘smokeless’ tobacco (snuff and chewing tobacco): significantly contribute to the development of head and neck cancer. This is especially true for cancers of the mouth, throat and larynx (voice box). Those who smoke and drink a lot of alcohol are at a much higher risk compared with those who only use either alcohol or smoking alone

  • infection with HPV (human papillomavirus): may contribute to the development of head and neck cancer, particularly those involving the tonsils or tongue base. The cancers in the tonsil and tongue base are usually small and difficult to detect, but have the ability to spread to enlarged lymph nodes in the neck and account for many cancers of unknown primary

  • ​sun exposure: contributes to skin cancer, the most common type of cancer in Australia. Patients with skin cancer often have had many primary cancers treated making it difficult to know whether a cancer in a lymph node has come from a skin cancer or not